Weidong Zheng

Large-scale synthesis of Li1.15V3O8 nanobelts and their lithium storage behavior studied by in situ X-ray diffraction

Li1.15V3O8 nanobelts with length 3 μm, width 200 nm and 20–50 nm in thickness are prepared on a large scale by a tartaric acid-assisted sol–gel technique. They show greater reversibility of the lithium ion insertion/extraction reaction than those synthesized without the addition of tartaric acid. After twenty cycles, the reversible lithium storage capacities of Li1.15V3O8 prepared from tartaric acid assisted and free techniques are 231.0 and 194.5 mAh/g at a current density of 30 mA g−1, respectively. Cycled at 20 mA g−1 in 1.5–4.1 V, Li1.15V3O8 nanobelts can deliver discharge and charge capacities of 297.0 and 298.4 mAh/g, respectively. Increasing the charge/discharge current density to 2400 mA g−1, the lithiation and delithiation capacities of Li1.15V3O8 nanobelts can be mantianed at 184.2 and 184.2 mAh/g, respectively. In situXRD observation reveals that the host structure of Li1.15V3O8 nanobelts will not be destroyed with a discharge process to 0.0 V at 20 mA g−1 or a short circuit for 24 h. Over-lithiation can induce the formation of an inactive compound, leading to poor electrochemical properties of Li1.15V3O8 nanobelts. The first lithiation/delithiation process in 0.0–4.1 V or 1.5–4.1 V is a reversible reaction at a current density of 60 mA g−1, and is composed of reversible single-phase structural evolutions in a high voltage region and two-phase structural transitions in a low voltage region. The electrochemical properties of Li1.15V3O8 nanobelts are poorer at the 10th cycle in 0.0–4.1 V than that obtained in 1.5–4.1 V. In situXRD results indicate that the breakdown of two-phase transition in a low voltage region is the main factor for poor cycleability. Besides, a delay of structural evolution and asymmetry lithiation/delithiation process can be observed at high rates, which may also be responsible for the deterioration of cycleability of Li1.15V3O8 nanobelts.

In situ fabrication of Li4Ti5O12@CNT composites and their superior lithium storage properties

In this paper, Li4Ti5O12@CNT composites are fabricated by a controlled in situ growth of CNTs on the surface of Li4Ti5O12. The formation of coiled CNTs occurs by the electroless loading of Ni–P catalysts on the surface of Li4Ti5O12. Coiled CNTs provide electron bridges interconnecting the Li4Ti5O12 particles to form a nano/micro-structured conductive hyper-network. The electronic conductivity of Li4Ti5O12@CNT composites is better than that of the sample before coating. As a result, Li4Ti5O12@CNT composites show superior lithium storage properties comparable to the pristine Li4Ti5O12. Based on electrochemical analysis, it is obvious that Li4Ti5O12@CNT composites can deliver reversible charge capacities of 149.2, 102.6, 73.3 and 47.5 mA h g−1 at 0.2 C, 10 C, 20 C and 50 C, respectively.

Facile fabrication of conducting hollow carbon nanofibers/Si composites for copper phthalocyanine-based field effect transistors and high performance lithium-ion batteries

In this paper, we describe the preparation and dual-use of carbon nanofibers/Si (CNFs/Si) composites as the source/drain contacts for copper phthalocyanine (CuPc) based thin film transistors (TFTs) and as anode materials for high performance lithium-ion batteries. The CNFs/Si composites are prepared by a facile chemical vapor deposition (CVD) technique with iron nitrate as the catalyst source and acetylene as the carbon source. In the CNFs/Si structure, Si particles are tightly wrapped by CNFs with an average diameter of 15–30 nm and length of 1–2 μm. It can be seen that the catalysts are grown on the top tip of the CNFs. Based on the superior properties of the CNFs coating, the CNFs/Si composites are applied in different fields. Compared with CuPc based OTFTs with Au contacts, the performances of organic thin film transistors (OTFTs) with CNFs/Si contacts are significantly improved. For OTFTs with CNFs/Si contacts, they show the on-state current increasing from 9 × 10−9 to 3 × 10−7 A at the gate voltage of −40 V, field effect mobility increasing from 1.9 × 10−4 to 4.2 × 10−3 cm2 V−1 s−1, and threshold voltage shifting from 15 to 30 V for the saturation regime. These are attributed to the more effective charge-carrier injection of CNFs/Si contacts than of Au contacts. Besides, the CNFs/Si composites are also promising lithium storage host materials. They show excellent rate capability as anode materials for lithium batteries. The initial discharge and charge capacities of CNFs/Si composites at 0.05 C are 1491.6 and 1168.7 mAh g−1, respectively. For comparison, the initial discharge and charge capacities of the CNFs/Si composites at 0.60 C are 1197.8 and 941.4 mAh g−1, respectively. After twenty cycles, the discharge and charge capacities at 0.60 C are 834.4 and 733.9 mAh g−1, respectively.

Facile controlled growth of silica on carbon spheres and their superior electrochemical properties

In this paper, silica coated carbon sphere composites were synthesized by a facile hydrothermal method. During the preparation, carbon@silica composites were formed by hydrolysis and deposition of TEOS on the surface of carbon spheres. XRD patterns show that this coating layer is composed of crystallized SiO2. When different amounts of TEOS were added, carbon@silica composites show different surface morphologies formed by silica nucleation and growth, spreading into a thinly coated layer, repeatedly. These varied silica coating layers have a great effect on the SEI film formation and electrochemical properties of the carbon@silica composites. The surface morphology and onset formation voltage of the surface film are greatly dependent on the surface morphology and structure of carbon@silica composites. Similarly, the lithiation and delithiation behaviors are obviously affected by this silica coating layer. Carbon@silica composites can deliver a reversible capacity of 351 mAh·g−1 in 0.0–3.0 V after 30 cycles, which is higher than that of the pristine carbon spheres. The extra capacity mainly comes from the Li-storage in the micropores and disordered graphene layers after silica coating. By broadening the electrochemical cycling window, a higher reversible capacity of 511 mAh·g−1 can be delivered in the voltage range between −15 mV and 3.0 V. The excess capacity in the low voltage region is mainly associated with additional Li-storage in micropores. It indicates that carbon@silica composites are promising anode materials for lithium-ion batteries.

LiNi1/3Co1/3Mn1/3O2 cathode materials for LIB prepared by spray pyrolysis. II. Li+ diffusion kinetics

Layered lithium ion battery cathode material LiNi1/3Co1/3Mn1/3O2 with a uniform particle size of about 6 μm was synthesized by a spray pyrolysis method. The lithium ion diffusion kinetics in LiNi1/3Co1/3Mn1/3O2 composite cathode were systematically studied by the ratio of potentio-charge capacity to galvano-charge capacity method, galvanostatic intermittent titration technique, electrochemical impedance spectroscopy, and potential step chronoamperometry methods. The variations of lithium ion diffusion coefficients obtained by the four methods show a close similarity. They vary in the range of 10−8 to 10−10 cm2 s−1, with a maximum at 4.1- to 4.2-V voltage level.